Gravity-induced loss of consciousness (G-LOC) refers to the situation in which a pilot loses consciousness because the amount of blood supplied to his or her head is not maintained due to increased acceleration caused by rapid flight maneuvering.
G-LOC affects the human body, including the cardiovascular system, ocular organs, and the like. Particularly, arterial pressure in the eye is directly affected by G-LOC. A decrease in arterial pressure in the eye means a decrease in the cerebral blood flow to the brain. Generally, the mean pressure in the cerebral arteries decreases by 22 to 25 mmHg for every +1 Gz increase in gravitational acceleration.
Meanwhile, such increased acceleration causes blood to be stagnant in the lower body, and the flow of venal blood to the heart is decreased, thus decreasing cardiac output. The cerebral arterial pressure, which is about 78 mmHg at +1 Gz under normal conditions, falls to −10 mmHg when a person is exposed to +5 Gz of gravitational acceleration, and this is the immediate cause of G-LOC. Also, in response to the decreases in the arterial pressure and the cardiac output, the heart rate sharply increases. Here, +5 Gz is five times the gravitational acceleration of +1 Gz.
The change that is most immediately sensed by a person who is exposed to high levels of acceleration is the change of vision. More specifically, due to the decrease in the pressure of the arteries connected to the eyes, insufficient oxygen is supplied to the retinas, whereby loss of vision may occur. The loss of vision is classified into gray-out, corresponding to loss of peripheral vision, and black-out, corresponding to loss of central vision, according to the phase, and such loss of vision signifies imminent G-LOC.
FIG. 1 shows average G-tolerance. In the state in which no specific apparatus or method is provided, when the G Level of gravitational acceleration (+Gz) rapidly increases from 1 Gz to 6 Gz or higher, or when a person is consistently exposed to gravitational acceleration of 6 Gz or higher, the person may suffer G-LOC within five seconds, as illustrated in FIG. 1.
Therefore, in order to prevent and overcome G-LOC, a pilot (in particular, a fighter pilot) needs to use a method for maintaining a consistent supply of blood to his or her head. As an example of such a method, there are a method of adjusting the angle of a pilot's seat in a fighter plane, a method of quickly contracting the lower limb muscles, such as the muscles of the legs and abdomen, while wearing an anti-G suit, an anti-G straining maneuver (AGSM) for maintaining or increasing the supply of blood to the brain by breathing according to a respiration method called an L-1 Maneuver, and the like.
However, aircraft accidents attributable to G-LOC continue to occur despite various efforts to improve G-tolerance against such increased gravitational acceleration, and reasonable and appropriate solutions have not yet been provided.